This invention can relate to antennas, and more particularly, to compact tunable antennas used in wireless handheld electronic devices.
Wireless handheld devices, such as cellular telephones, contain antennas. As integrated circuit technology advances, handheld devices are shrinking in size. Small antennas are therefore needed.
A typical antenna for a handheld device is formed from a metal radiating element. The radiating element may be fabricated by patterning a metal layer on a circuit board substrate or may be formed from a sheet of thin metal using a foil stamping process. These techniques can be used to produce antennas that fit within the tight confines of a compact handheld device.
Modern handheld electronic devices often need to function over a number of different communications bands. For example, quad-band cellular telephones that use the popular global system for mobile (GSM) communications standard need to operate at four different frequencies (850 MHz, 900 MHz, 1800 MHz, and 1900 MHz).
Although multi-band operation is desirable, it is difficult to design a compact antenna that functions satisfactorily over a wide frequency range. This is because small antennas tend to operate over narrow frequency ranges due to the small dimensions of their radiating elements.
Antennas with tunable capacitive loading have been developed in an attempt to address the need for compact multi-band antennas. By varying the amount of capacitive loading that is applied to the radiating element, the resonant frequency of the antenna can be adjusted. This allows an antenna with a relatively narrow frequency range to be tuned sufficiently to cover more than one band.
The adjustable capacitive loading that is placed on this type of antenna leads to unwanted power loss. As a result, capacitively-tuned antennas tend to exhibit less-than-optimal efficiencies.
It would be desirable to be able to provide ways in which to improve the performance of tunable antennas for handheld electronic devices.